This invention relates to a bushing base plate having a box filled with melted glass or a nozzle aperture of a bushing employed for preparing glass fibers or continuous glass filaments.
Several plates are currently employed as a bushing base plate. Generally, the bush base plate is prepared by conducting a perforation treatment of a bashing base raw plate and inserting a hollow tube processed in advance to the shape of a pipe into the aperture of the raw plate and bonded by means of welding. Another bushing base plate which is prepared by compressing raw material having a plate thickness thicker than that of a final product by means of rolling or pressing to extrude a projection, and thereafter conducting a perforation treatment to the extruded projection by means of pressing is also employed.
A glass fiber of thin denier and an effective production thereof by making many holes in a certain area with smaller pitches are demanded and a bushing base plate satisfying these requirements is highly requested.
When conventionally welding is conducted by making an aperture through the bushing base raw plate and inserting the hollow tube processed in advance to the shape of a pipe into the aperture of the raw plate, the bushing base raw plate 1 and the hollow tube 3 having a flow-out aperture 2 are as shown in FIG. 1 are welded at the base end of the hollow tube 3 by means of razor or plasma or resistive welding.
In this case, the hollow tube 3 in the shape of a pipe is finished so as to have a thin wall due to the spinning conditions of glass fibers. When the hollow tube is welded to the position perforated through the bushing base raw plate 1, the welding is performed at the base end 3a of the hollow tube 3 that is the flow-in side of the glass as shown in FIG. 1.
Since the wall thickness of the hollow tube 3 is thinner than the thickness of the bushing base raw plate 1, the size of the flow-out aperture is small and the pitch between two adjacent flow-out apertures is small so that the whole thickness of the bushing base raw plate 1 is difficult to be welded, only an upper portion of the raw plate 1 is welded as shown in FIG. 1. Because of this partial welding, the flow-out aperture is difficult to be processed to the shape which fits the flow conditions of glass or the spinning conditions.
When the thus manufactured bushing case plate 4 is employed successively for a long period of time at a high temperature, a creep strain is produced in the bushing base plate 4 receiving a pressure P of glass to be entirely deformed so as to have a swelling as shown in FIG. 2.
FIG. 3 is an enlarged view showing the above fitting portion of the hollow tube 3. Due to the creep deformation of the bushing base raw plate 1, a space is formed between the raw plate 1 and the hollow tube 3 to produce a crack at the above welded portion so that a drawback of enabling the glass fiber spinning because of the leakage of glass liquid. In the worst case, the hollow tube 3 may fall off.
This drawback is critical because even when only one of the flow-out apertures is cracked or falls off, an expensive Pt alloy bushing can be no longer employed so as to stop the production or the bushing with the defect may largely influence the quality and the cost of the glass fibers. It is a problem to be solved how to provide a bushing in which cracking and the falling off are difficult to occur.
A new process of preparing a bushing is proposed in Japanese laid open gazette No. 4-241105 or the like. This contemplates to perform the bonding employed Pt waxy material to the Pt alloy base plate. When a small amount of an element is added to Pt in case of a Pt--Au alloy or a reinforced alloy, that is, when the material possesses a melting point which is the same as or smaller than that of Pt as waxy material, it is supposed to be difficult to melt the Pt by employing Pt as the waxy material.